Engineering topics

Pater, R. H.

Publications and source records attributed to Pater, R. H..

17 records

NASA NTRS1996

A Method for Characterizing Thermoset Polyimides

Thermoset polyimides have great potential for successfully meeting tough stress and temperature challenges in the advanced aircraft development program. However, studies of structure-property relationships in these materials have not been very successful so far. Positron lifetime spectroscopy (PLS) has been used to investigate free volumes and associated parameters in a series of variable, segmental molecular weight samples. The free volume correlates well with the molecular weight M(sub c), the cross-link density v, and the coefficient of thermal expansion (CTE) of these materials. Currently, no other techniques are available for direct measurement of these parameters, particularly for polymers in solid phase. Experimental results and their interpretations are presented.

Ranganathaiah, C.↗

NASA NTRS1994

Morphology of Thermoset Polyimides by Positron Annihilation Spectroscopy

Thermoset polyimides have great potential for successfully meeting tough stress and temperature challenges in the advanced aircraft development program. However, studies of structure/property relationships in these materials have not been very successful so far. Positron annihilation spectroscopy has been used to investigate free volumes and associated parameters. It has been noted that the free volume correlates well with the molecular weight, cross-link density and thermal coefficient of expansion of these materials. Currently no other techniques are available for direct measurement of these parameters. Experimental results and their interpretations will be discussed.

Ranganathaiah, C.↗

NASA NTRS1991

Crosslinking-property relationships in PMR polyimide composites. I

The effect of the crosslink density of the matrix on physical and mechanical properties of a graphite-fiber-reinforced PMR (for polymerization of monomer reactants) polyimide composites during isothermal aging was investigated in experiments where unidirectional composite specimens of Celion 6000/PMR-P1 were isothermally exposed at 288 C in air for various time periods up to 5000 hrs. It was found that, as the crosslink density increased, the glass transition temperature, density, and elevated-temperature interlaminar shear strength of a composite increased, while the initial moisture absorption and the coefficient of thermal expansion decreased. However, after reaching the highest possible matrix crosslink density, several of the composite properties began to deteriorate rapidly.

Pater, R. H.↗

NASA NTRS1991

High performance addition-type thermoplastics (ATTs) - Evidence for the formation of a Diels-Alder adduct in the reaction of an acetylene-terminated material and a bismaleimide

Recently, the concept and demonstration of a new versatile synthetic reaction for making a large number of high-performance addition-type thermoplastics (ATTs) were reported. The synthesis shows promise for providing polymers having an attractive combination of easy processability, good toughness, respectable high temperature mechanical performance, and excellent thermo-oxidative stability. The new chemistry involves the reaction of an acetylene-terminated material with a bismaleimide or benzoquinone. In order to clarify the reaction mechanism, model compound studies were undertaken in solutions as well as in the solid state. The reaction products were purified by flash chromatography and characterized by conventional analytical techniques including NMR, FT-IR, UV-visible, mass spectroscopy, and high pressure liquid chromatography. The results are presented of the model compound studies which strongly support the formation of a Diels-Alder adduct in the reaction of an acetylene-terminated compound and a bismaleimide or benzoquinone.

Pater, R. H.↗

NASA NTRS1991

Freeze-drying for morphological control of high performance semi-interpenetrating polymer networks. III

The feasibility of using a freeze-drying (solvent removal by sublimation) approach for controlling the morphology of a high-performance semi-IPN is assessed. A high-performance thermoplastic polyimide and commercially available 4,4'-bismaleimide diphenylenemethane were dissolved in a solvent, 1,3,5-trioxane. The solvent was removed from the constituents by freeze-drying. For purposes of comparison, the constituents were dissolved in a high-boiling-point solvent, N,N-dimethylformamide. The solvent was removed from the solution by evaporation. The physical and mechanical properties and phase morphology of the neat resins and composites prepared by freeze-drying and traditional solution methods are presented and compared. It is concluded that the TG is higher and that the magnitude of minor constituent separation is less in the freeze-dry processed materials than for the processed solution.

Hsiung, H. J.↗

NASA NTRS1990

Film properties of high performance semi-interpenetrating polyimide networks

Consideration is given to an approach to provide a semi-IPN in which two constituent materials have nearly the same chemical structure and polymer chain length. A reactive endcapped LARC-TPI polyamic acid having a formulated molecular weight of 20,000 is prepared and then combined with various quantities of a commercial LARC-TPI polyamic acid solution. The polyimide films of semi-IPNs are tested along with two constituent materials. The physical and mechanical properties of the polyimide films are presented. The applicability of using this approach to minimize phase separation and to maximize long-term phase stability is discussed. The concept of controlling morphology by chemistry is proven for providing LARC-TPI based semi-2-IPNs. A very long chain LARC-TPI endcapped with a nadic group exhibits physical properties almost identical to unendcapped LARC-TPI.

Gerber, M. K.↗

NASA NTRS1987

Crosslinking-property relationships in PMR polyimide composites. I

The thermooxidatively-induced crosslinking/ physical and mechanical property relationships of graphite fiber-reinforced PMR polyimide-matrix composites were studied during isothermal exposure of the composite specimens at 288 C in air for periods of up to 5000 hr. The crosslinking densities due to this treatment were estimated on the basis of the kinetic theory of rubber elasticity and shifts in the glass transition temperature T(g). Several linear relationships are noted between crosslink density and physical and mechanical properties: T(g), initial weight loss, and elevated temperature interlaminar shear strength increase with crosslink density, while initial moisture absorption decreases. After achieving the highest crosslink density, several of the composite properties begin to decrease from their maximum values.

Pater, R. H.↗

NASA NTRS1985

High temperature resistant polyimide from tetra ester, diamine, diester and N-arylnadimide

The invention described relates to improved polyimide resins which are noted for their high thermal and oxidative stability, high strength at elevated temperatures and which exhibit many other outstanding physical and chemical properties, especially useful in high temperature applications. The polyimides are prepared by the reaction, with application of heat of a mixture of monomers comprising: (1) a dialkyl or tetraalkyl ester of an aromatic tetracarboxylic acid, (2) and aromatic diamine, (3) a monoalkyl or dialky ester of a dicarboxylic acid, and (4) a N-arylnadimide such as N-phenylnadimide. Polyimides of monomers (1), (2) and (3) are known.

Pater, R. H.↗

NASA NTRS1985

Rheological, processing, and 371 deg C mechanical properties of Celion 6000/N-phenylnadimide modified PMR composites

The rheology, processing, and chemistry of newly developed N-phenylnadimide modified PMR (PMR-PN) polyimide resins are reviewed. The 371 C performance of their composites reinforced with Celion 6000 graphite fibers is also reviewed, along with the state of the art Celion 6000/PMR-15 composite. The effects of the 371 C exposure in air for up to 300 hr on the composite glass transition temperature, weight loss characteristics, and dimensional stability are presented. The changes in the composite 371 C interlaminar shear and flexural properties are also presented. In addition, composite interfacial degradation at a function of exposure time at 371 C was followed by scanning electron microscopy. The results suggest that the composite materials can be used at 371 C for at least 100 hr.

Pater, R. H.↗

NASA NTRS1983

High-Performance Matrix Resins

State-of-the-art PMR polyimides provide good strength and light weight in wide variety of critical applications. However, improved processability and elevated temperature thermo-oxidative stability are desired in such polyimide systems. Resins, intended for use in advanced composites, adhesives, and neat resin articles, show improvements in both processability and elevatedtemperature stability over state-of-the-art PMR-15 polymers.

Pater, R. H.↗

NASA NTRS1983

Dynamic Mechanical Properties of N-Phenylnadimide Modified PMR Polyimide Composites

The rheological behavior of newly developd Celion 6000/N-phenylnadimide modified PMR polyimide and PMR-15 composites was investigated. The dynamic mechanical properties were correlated with the structure of N-phenylnadimide modified PMR polyimides. The storage modulus (G'), loss modulus (G''), and loss tangent (tan delta) of four composite systems were measured over a temperature range from -150 to 400 C. Three well defined peaks were seen in the regions of 360, 100, and -120 C, corresponding to the alpha, beta, and gamma relaxations, respectively, of the matrix resins. The activation energies of the alpha, beta, and gamma relaxations were estimated to be 232, 60, and 14 kcal/mole, respectively, for PMR-15. Addition of N-phenylnadimide to the PMR-15 composition lowered the glass transition temperature and the activation energies of PMR-15 polyimide. The dynamic mechanical data appear to be consistent with the formation of a copolymer from N-phenylnadimide and a PMR-15 prepolymer.

Pater, R. H.↗

NASA NTRS1982

The properties of novel bisimide amine cured epoxy/Celion 6000 graphite fiber composites

The study is concerned with the further development of bisimide amine cured epoxy resins first reported by Serafini et al. (1979). Attention is given to properties of the neat resins and composites made with these novel epoxy resins and Celion 6000 graphite fibers. The use of bisimide amine hardeners to cure epoxy resins causes a significant improvement in the char-forming characteristics of the cured resin. Compared to epoxy resins cured with a conventional amine, such as 4,4'-diaminodiphenylsulfone, the bisimide cured epoxies exhibit about a twofold improvement in the aerobic char yield at 800 C. The levels of moisture absorption exhibited by the bisimide amine cured epoxies were found to be considerably lower than those exhibited by state-of-the-art epoxies (0.5 wt.% versus 2.0%).

Scola, D. A.↗

NASA NTRS1982

The 371 deg C(700 deg F) properties of celion 6000/n-phenylnadimide modified PMR polyimide composites

The 371 C (700 F) properties of Celion 6000/N-phenylnadimide modified PMR-15 polyimide composites were investigated to determine the feasibility of using these materials at a 371 C (700 F) service temperature. The processing characteristics and physical and mechanical properties of the composite systems are presented. The results of the 371 C (700 F) thermo-oxidation stability study suggest that the composite materials can be considered for short term (at least 100 hours) application at 371 C (700 F).

Pater, R. H.↗

NASA NTRS1981

Novel improved PMR polyimides

The development of a class of high-temperature-resistant resins known as PMR polyimides has been reported by Serafini et al. (1972). Serafini and Vannucci (1975) found that the lower formulated molecular weight (FMW) compositions exhibited increased resin flow, but with some sacrifice in elevated temperature thermo-oxidative stability. Vannucci (1977) reported that the resin flow characteristics of the PMR composition having an FMW of 1500 could be varied by controlling the degree of resin advancement or imidization. The current investigation is concerned with an alternative approach to obtain improved flow PMR polyimides without sacrificing the desirable thermo-oxidative characteristics. The new approach is based on the utilization of a chemically compatible flow modifying agent. This agent is N-phenylnadimide (PN). The determination of the processing characteristics and properties of PN modified PMR/Celion 6000 composites is discussed.

Pater, R. H.↗

NASA NTRS1981

Imide modified epoxy matrix resins

High char yield epoxy using novel bisimide amines (BIA's) as curing agents with a state of the art epoxy resin was developed. Stoichiometric quantities of the epoxy resin and the BIA's were studied to determine the cure cycle required for preparation of resin specimens. The bisimide cured epoxies were designated IME's (imide modified epoxy). The physical, thermal and mechanical properties of these novel resins were determined. The levels of moisture absorption exhibited by the bisimide amine cured expoxies (IME's) were considerably lower than the state of the art epoxies. The strain-to-failure of the control resin system was improved 25% by replacement of DDS with 6F-DDS. Each BIA containing resin exhibited twice the char yield of the control resin MY 720/DDS. Graphite fiber reinforced control (C) and IME resins were fabricated and characterized. Two of the composite systems showed superior properties compared to the other Celion 6000/IME composite systems and state of the art graphite epoxy systems. The two systems exhibited excellent wet shear and flexural strengths and moduli at 300 and 350 F.

Scola, D. A.↗

NASA NTRS1981

Novel improved PMR polyimides

A series of N-phenylnadimide (PN) modified PMR polyimide composites reinforced with graphite fibers was investigated. The improved flow matrix resins consist of N-phenylnadimide (PN), monomenthyl ester of 5-norbornene-2, 3-dicarboxylic acid (NE), dimethyl ester of 3,3, 4,4-benzophenonetetracarboxylic acide (BTDE), and 4,4 methylenedianiline (MDA). Five modified PMR resin systems were formulated by the addition of 4 to 20 mole percent N-phenylnadimide to the standard PMR-15 composition. These formulations and the control PMR resin were evaluated for rheological characteristics. The initial thermal and mechanical properties of the PN modified PMR and the control PMR/Celion 6000 composites were determined. The results show that the addition of N-phenylnadimide to PMR-15 significantly improved the resin flow characteristics without sacrificing the composites properties. Concentrations of 4 and 9 mole percent PN appear to improve the thermoxidative stability of PMR composites.

Pater, R. H.↗

NASA NTRS1978

Synthesis of improved moisture resistant polymers

The synthesis and characterization of novel moisture resistant aliphatic polyimides are described. Several novel aliphatic imides of diversified functionalities were synthesized, purified, and characterized, they include: (1) N-(12-aminododecyl)-5-norbornene-2,3-dicarboximide; (2) N,N'-2,2,2-trifluoro-1-(trifluoromethyl)ethylidene bis (1,3-dioxo-5,2-iosoindolinediyl)dodecamethylene di-5-norbornene-2,3-dicarboximide; (3) N,N'-dodecamethylenedi-5-nobornene-2,3-dicarbonoximide; (4) N,N'-dodecamethylenebis 5,6-epoxy-2,3-norbornanedicarboximide ; and (5) N,N'-Bis 12-(5-norbornene-2, 3-dicarboximidido)dodecyl - 1,2,3,4- butanetetracarboxylic 1,2:3,4-diimide. The structures of these compounds were established by elemental analysis, IR, NMR, and mass spectra.

Scola, D. A.↗